Currently used high-pressure discharge lamps usually include metal halides to obtain desired color rendition. The metal halides have the characteristic that, in dependence on the particular type of halide used, and the quantity of the metal halide in the discharge chamber defined by the discharge vessel, their presence can lead to corrosion of the electrodes. Corrosion at the electrode results in removal of material from the electrode shafts. This material removal may continue to such an extent that the electrode shaft is sufficiently weakened, leading, eventually, to breakage of the electrode, and, hence, failure of the lamp.
U.S. Pat. No. 4,633,136, Fromm et al. assigned to the assignee of the present application and the disclosure of which is hereby incorporated by reference, describes a metal halide high-pressure discharge lamp in which, to strengthen the electrode shaft, the electrode shaft is surrounded by a cover of high temperature resistant metal. This cover is formed as a conical spiral or coil, in which the individual windings of the coils are placed closely against each other, and have one end thereof melted into the discharge vessel, for example into the press seal through which the electrode shaft extends. The presence of this coiled winding decreases material loss on the electrode by corrosion caused by the metal halides at the transition point between the electrode shaft and the press or pinch seal.